1. Field of the Invention
This invention relates to a printed circuit board having means for decreasing electromagnetic radiation emitted therefrom, an information processing apparatus having such printed circuit board(s), and a method for adjusting a suitable combination of the circuits arrangement to reduce the electromagnetic radiation.
More particularly this invention relates to decreasing electromagnetic radiation from mobile terminals, such as mobile computers and notebook computers, having a function of data communication with other facilities with a wireless interface.
2. Description of the Related Art
In recent years, higher performances of the apparatus need higher clock frequencies to operate CPU and electronic components in the apparatus. And the higher clock frequencies cause higher speed variations of voltage pulses between a voltage layer and a ground layer in printed circuit boards (PCBs) in the apparatus; and, therefore, electromagnetic radiation is radiated from the boards.
On the other hand, the development in computer downsizing has resulted in so called mobile computers, notebook computers, and laptop computers, which are easily carried. And these small sized computers can also communicate with other facilities with wireless interfaces. As these apparatus with wireless interface are particularly susceptible to the electromagnetic radiation emitted therefrom, it is very important to reduce the electromagnetic radiation.
As the electromagnetic radiation maybe cause erroneous operations in other nearby facilities, there are usually provided metallic shieldings covering the apparatus and containment arrangements on the PCBs to reduce the radiation. To more successful development in the apparatus, it is preferable to reduce the electromagnetic radiation from PCBs itself, because it is possible to reduce the electromagnetic radiation without increasing the metallic shielding structures, which adversely affect the computer downsizing.
One of the containment arrangements has been proposed in Japanese Patent Application No. 08-073987 (Unexamined Patent Publication No. 09-266361), where a PCB structure includes capacitors connected between a voltage layer and a ground layer at the border portion of the PCB. As the capacitors act as by-pass capacitors, the electromagnetic radiation caused from the voltage oscillation is reduced. In spite of preventing the electromagnetic radiation without affecting the scale of PCB""s size, the prior art has traditional drawbacks described hereinafter, as the capacitance values and locations of the by-pass capacitors are fixed. That is, even in the prior art it must take laborintensive practice to adjust in a short time the characteristics of circuits for the reducing electromagnetic radiation, according to the rapid progress of computers, such as adoption of higher operating frequency in CPU. After redesigns and trial productions, values of capacitors and their locations on PCBs are decided.
A conventional design method to prevent the electromagnetic radiation is a manner of a cut-and-try one. After a number of trials, metallic shielding structures or characteristics of electronic components such as capacitors used in the circuits preventing electromagnetic radiation are decided. This conventional design method takes long time troublesome working to decide specifications of parts and components, and it is necessary to redesign the circuits to reduce the electromagnetic radiation in almost every case of changing a design of apparatus or other circuit configuration.
As undesired electromagnetic radiation from electro-equipment result in electromagnetic interference (xe2x80x9cEMIxe2x80x9d), a circuit for reducing the electromagnetic radiation is referred to hereinafter designate as an xe2x80x9cEMI reducing circuit.xe2x80x9d
An object of this invention is to provide a PCB having an improved arrangement of EMI reducing circuits each of which includes a circuit element for decreasing electromagnetic radiation form the PCB and a switching device selectively connecting the circuit element to a portion of a printed circuit pattern for enabling and disabling the circuit element. In preferred embodiment for the object of the present invention, the PCB has a plurality of EMI reducing circuits comprising a bypassing circuit or damping circuit, and a switching device. The switching device is connected to the bypassing circuit or the xe2x80x9cdamping circuit, and is for enabling and disabling the bypassing circuit or the damping circuit. Further object of this invention is to provide an information processing apparatus having a function minimized electromagnetic radiation. In preferred embodiment for the further object of the present invention, the apparatus has the above mentioned PCB and further comprises a memory device for storing information of a plurality of predetermined combination of the EMI reducing circuits to be enabled and disabled, and a control unit for transmitting signals to the EMI reducing circuits for opening or closing the switching devices corresponding to the information stored in the memory device.
Still another object of this invention is to provide a mobile terminal having the PCB(s) and a detachable wireless communication module. In preferred embodiment for the still another object of the present invention, the mobile terminal further includes the memory device, the control unit, a data storing device for storing original data, a comparing unit for obtaining a difference between the original data and a data received by the communication means by comparing these data, and a means for selecting a minimum difference out of a plurality of the differences and transmitting a data of the combination of the EMI reducing circuits resulting in the minimum difference to the control unit. Still another object of this invention is to provide a method for adjusting a suitable combination of the circuit characteristics in a mobile terminal used for data communication. In preferred embodiment for the still another object of the present invention, the method for adjusting the EMI reducing circuits mounted on a printed circuit board comprises a step of composing a plurality of combination of the EMI reducing circuits to be enabled or disabled, a step of performing information processing in enabling the EMI reducing circuits in each of the combination, a step of measuring electromagnetic radiation emitted from the printed circuit board in performing the information processing, a step of comparing amounts of the electromagnetic radiation, a step of selecting a minimum amount out of the amounts, and a step of enabling the EMI reducing circuits of the selected combination resulting in the minimum amount.
Other objects and advantages of the present invention will be apparent from the following description, the appending claims and accompanying drawings.